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Date:   Thu, 14 Oct 2021 22:45:52 -0500
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Subject: Re: [PATCH v1 2/2] mm: remove extra ZONE_DEVICE struct page refcount
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To:     Ralph Campbell <rcampbell@nvidia.com>,
        Jason Gunthorpe <jgg@nvidia.com>
Cc:     akpm@linux-foundation.org, Felix.Kuehling@amd.com,
        linux-mm@kvack.org, linux-ext4@vger.kernel.org,
        linux-xfs@vger.kernel.org, amd-gfx@lists.freedesktop.org,
        dri-devel@lists.freedesktop.org, hch@lst.de, jglisse@redhat.com,
        apopple@nvidia.com, willy@infradead.org
References: <20211014153928.16805-1-alex.sierra@amd.com>
 <20211014153928.16805-3-alex.sierra@amd.com>
 <20211014170634.GV2744544@nvidia.com>
 <eafbccb5-f94b-0ddd-bb46-7ee92ed36ee8@nvidia.com>
 <20211014180132.GA3567687@nvidia.com>
 <b8b57851-674a-956d-0d7a-779e601bf6d8@nvidia.com>
From:   "Sierra Guiza, Alejandro (Alex)" <alex.sierra@amd.com>
In-Reply-To: <b8b57851-674a-956d-0d7a-779e601bf6d8@nvidia.com>
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On 10/14/2021 3:57 PM, Ralph Campbell wrote:
>
> On 10/14/21 11:01 AM, Jason Gunthorpe wrote:
>> On Thu, Oct 14, 2021 at 10:35:27AM -0700, Ralph Campbell wrote:
>>
>>> I ran xfstests-dev using the kernel boot option to "fake" a pmem device
>>> when I first posted this patch. The tests ran OK (or at least the same
>>> tests passed with and without my patch).
>> Hmm. I know nothing of xfstests but
>>
>> tests/generic/413
>>
>> Looks kind of like it might cover this situation?
>>
>> Did it run for you?
>>
>> Jason
>
> I don't remember. I'll have to rerun the test which might take a day 
> or two
> to set up again.
>
I just ran this generic/413 on my side using pmem fake device. It does fail.
I remember we proposed a fix on this patch before try_get_page was removed.
@@ -1186,7 +1153,7 @@ bool __must_check try_grab_page(struct page *page, 
unsigned int flags);
  static inline __must_check bool try_get_page(struct page *page)
  {
         page = compound_head(page);
-       if (WARN_ON_ONCE(page_ref_count(page) <= 0))
+       if (WARN_ON_ONCE(page_ref_count(page) < 
(int)!is_zone_device_page(page)))
                 return false;
         page_ref_inc(page);
         return true;

Alex